Stephen Max

iTrader: (59)

I made a simple pressure drop measuring setup using a Dwyer manometer and my Sears shop vac and tested my old HKS muffler and an Apexi WS muffler I recently acquired.

The test setup consisted of threading a hose barb into a spare test pipe and attaching one end of the manometer to the hose barb. The other end of the manometer was left exposed to ambient pressure. The test pipe was then bolted to the muffler flange. The shop vac was attached to the other end of the test pipe.

With the shop vac pulling air through the muffler, the manometer measures the pressure drop at the test pipe. A high pressure drop indicates high flow losses through the muffler, conversely a low pressure drop indicates low flow losses. In this way the resistance to flow between the two mufflers can be compared, at least at a qualitative level.


Results:

The test pipe by itself produced a pressure drop of .5 inches of water
The Apexi muffler and test pipe produced a pressure drop of 1.3 inches of water.
The HKS muffler and test pipe produced a pressure drop of 2.5 inches of water.

Conclusion:

The Apexi WS muffler produces less resistance to flow than the HKS muffler.

Comments:

The Apexi muffler is considerably newer than the HKS, perhaps carbon buildup in the HKS is affecting the results.
The experiment was done at one flow rate only.
The direction of flow through the muffler is reversed during the test.

Further work:

I am going to do the same test to my stock 4th gen muffler, and also a comparison of the Stillen b-pipe against the Apexi b-pipe.

Mizeree_X

iTrader: (9)

Excellent work. 1PSI = 27.7 in H2O, so the difference in pressure drop between the two mufflers is still pretty low. Also, I forget the relationship between pressure drops and fluid velocities, so if it is possible to get the Shop-Vac to run at different speeds (or use a blower instead), you could get even more useful information.

Stephen Max

iTrader: (59)

Yeah, I'm thinking a more useful test would be to just measure backpressure at WOT with the muffler on the car. But that involves more work, too. However, since I'm about to remove my Stillen b and stock muffler and put on the Apexi catback, I think I will do just that for a before and after comparison. I already have a MAP sensor on my car for datalogging boost, so I can just connect the MAP sensor to the exhaust pipe and datalog the results vs rpm.

krismax

iTrader: (15)

Great work! You are a genius. People bring him your mufflers.

Matt93SE

iTrader: (44)

LOL

If you're bored next time, I've got a cheapo fart cannon you can have to play with..

IceY2K1

iTrader: (3)

I think we need to get you a 5th gen muffler and lay that to rest.

Bags

iTrader: (3)

good stuff stephen

Terran

iTrader: (6)

Wouldn't the flow going in the wrong direction potentially give misleading info?

Stephen Max

iTrader: (59)

Possibly. It depends on how the internal baffles are made. For instance, the Flowmaster Delta series muffler has a V shaped baffle that would probably produce more resistance to flow if the flow was reversed.

At the low flow rate I tested the mufflers at, though, I think the direction of flow makes very little difference.

Stephen Max

iTrader: (59)

I got around to doing this over the weekend.

I ran a vacuum line from a fitting at the rear O2 sensor bung to the MAP sensor and tested the Stillen b pipe with oem 4th gen muffler, then installed the Apexi WS catback and repeated the test. Both tests were done at WOT in 2nd gear up to about 7000 rpm.

Results:

Backpressure in the Stillen b pipe and oem muffler combination was over 14.7 psig by the time I got to 6000 rpm. Unfortunately, I only have a 2 bar MAP sensor, so once the exhaust pressure hit 14.7 gauge psi the voltage signal flatlined. However, I had my boost gauge teed into the same line, and I saw about 17 psig just before ending the run.

With the Apexi catback, the maximum pressure recorded was 10 psig. At 6000 rpm the pressure was 8.4 psig (compared to the 14.7 psi at 6000 rpm with the oem muffler).

So there is a 6.3 psi difference at 6000 rpm and an estimated 7 psi difference at 7000 rpm.

Edit: I should mention that I'm running about 12 psi of boost at 7000 rpm, so I'm making considerably more exhaust flow than a NA engine. YMMV.